DESCRIPTION (adapted from the Abstract): The Principal Investigator offers the premise that certain homosexual/bisexual men and heterosexual women in New York City represent suitable populations for future vaccine efficacy trials to stem the sexually-transmitted HIV infection. In this project, she proposes to gather baseline data to assess this premise. Her aims are to: (1) enroll into a prospective study a cohort of seronegative adults--1358 homosexual men and 353 women--who are still likely to engage in high risk sexual activity; (2) determine the incidence of HIV infection in study participants during 18 months of follow-up; (3) assess risk behavior at enrollment, monitor changes in risk behavior, and assess the effect of such changes on the incidence of HIV infection; (4) determine lost-to-follow-up rates and monitor protocol adherence; (5) assess potential willingness to participate in future HIV vaccine trials; (6) assess adherence to a multi-dose vaccination schedule and reporting of side effects by offering hepatitis B vaccine to all enrolled participants who are HBV-susceptible; (7) work with community organizations to provide advice about the conduct of the study; and (8) establish the infrastructure, trained personnel, and community support for future HIV vaccine trials. To accomplish these goals, the Investigator and her associates will recruit candidates for the study from a variety of sources, including--but not limited to--the New York City Department of Health clinics for sexually-transmitted diseases (STD's) and anonymous counseling and testing sites, the Community Health Project, and St. Vincent's Hospital Early Intervention Project. Seronegative candidates who consent will return at 3- month intervals for 18 months so as to be monitored for their risk behavior and incidence of HIV infection. If the incidence of HIV infection is sufficiently high and other indices confirm the Investigator's premise, she will use the data generated to design future HIV vaccine efficacy trials.